A cargo handling system conveys and secures containerized and palletized cargo on an aircraft for fast and easy loading and unloading. Cargo systems are installed on the lower deck on passenger aircraft and also on the main deck of freighter aircraft. A typical system consists of conveyor rollers and tracks, or roller trays, side rail guides, side and end latches, power drive units (“PDUs”) and a PDU control unit. Additional components, such as various braking mechanisms, help limit movement of cargo during loading and unloading.
Items that are shipped by air typically are loaded first onto specially configured pallets, or into specially configured containers. In the air freight industry, these various pallets and containers are commonly referred to as Unit Load Devices (“ULDs”). ULDs are available in various sizes, shapes and capacities. Airlines can load and unload ULDs multiple times per day.
To facilitate movement of a ULD within an aircraft's cargo compartment, as the ULD is loaded, stowed, and unloaded, the deck of an aircraft cargo compartment typically includes a number of raised roller elements. These roller elements often include elongated roller trays that extend longitudinally along the length of the cargo deck, ball panel units, and the like. For example, roller trays typically include elongated rows of cylindrical rollers that extend in a fore and aft direction. Ball panel units include plates with upwardly protruding rotatable spherical balls. The ULDs sit atop these roller elements, and the roller elements facilitate rolling movement of the ULDs within the cargo compartment. The apex of these roller elements can form what is known in the art as the conveyor plane. The conveyor plane also refers to a bottom plane on which a ULD (with a completely fiat underside) traverses.
Unwanted movement of ULDs during loading and unloading can be a safety risk to the loaders. This unwanted movement may also cause damage to the aircraft's cargo compartment. Typically, a loader manually moves a ULD into and from its stowage position. Such movement can result regardless of whether the ULD is being manually loaded or unloaded, or being driven by a PDU. Braking mechanisms are installed on the floor of the cargo compartment to help protect cargo loaders and the aircraft from possible damage during loading and unloading. These braking mechanisms help control unwanted movement of the ULDs during these loading and unloading cycles.
A typical braking mechanism is a braking caster. A braking caster can have a rotating element that protrudes above the conveyor plane and is typically installed near the cargo door. The rotating element of the braking caster is configured to slow and stop a ULD, but allow travel when the ULD is manually or power driven. To accomplish this, the rotating element must be elevated above the conveyor plane to provide sufficient cargo contact and normal force for braking. However, the height at which the rotating element must be positioned can in fact lead to undesired damage to a ULD or the aircraft. Thus, a need has arisen for a rolling mechanism that facilitates or restricts cargo movement while minimizing the opportunity for damage to the cargo or aircraft during loading, unloading or transport.